There has been increased interest in the use of lasers for remote detection of underwater objects. Such technology is of high interest to the United States Navy for uses such as mine detection, location, and identification, and has significant potential for civilian use in detecting other underwater objects and seafloor features as well.
Conventional sonar systems rely on acoustical pulses generated from arrays of acoustic transducers towed through the water using either a ship or a helicopter. Towing speeds for such systems are limited to a few tens of knots, and therefore covering a large area can take considerable time and resources. Lasers, on the other hand, can be deployed from aerial sources such as helicopters and therefore can enable the search of much larger areas in much less time than conventional ship-based sonar systems. Additionally, the availability of suitable high repetition rate lasers, and the ease of directing laser beams with moveable mirrors, allow for rapid generation of acoustic sources over a large area and the efficient use of multi-static acoustic scattering sonar techniques. Thus, such systems can enable search rates that are several orders of magnitude faster than conventional sonar systems.
The Navy's Airborne Laser Mine Detection System (ALMDS) is an all optical system that uses LIDAR (Light Detection and Ranging) technology to detect, localize, and identify objects such as mines underwater.
Another technique developed by the Navy is an opto-acoustic technique using both laser acoustic generation and laser-Doppler vibrometry for receiving scattered acoustic pulses. See U.S. Pat. No. 7,259,864 to Antonelli et al. A related all-optical technique is outlined in Antonelli et al., “Experimental Investigation of Optical, Remote, Aerial Sonar,” Proc. 2002 Oceans MTS/IEEE Conf, 4 (October 2002) 19491955 and in Blackmon et al., “Remote, Aerial, Opto-acoustic Communications and Sonar,” Proc. SPIE Conf on Sensors and C3I for Homeland Security and Homeland Defense IV, 5778 (2005) 800.